Many people, and other mammalian animals, suffer from asthma, rhinitis and other diseases caused by the inhalation of aeroallergens. In order to understand the nature of the disease and possible treatments it would be desirable to be able to collect these aeroallergens from the inhaled air stream. Such collections could also act as a prophylactic measure.
While there is strong epidemiological evidence associating exposure to aeroallergens to both sensitisation and symptoms at a communal level, and to a lesser extent at an individual level, the methods for estimating personal exposure to aeroallergens are poorly developed. The most common method is to measure allergen concentration in settled dust (collected by a vacuum cleaner) which functions as a source of aeroallergens. The method has, however, serious confounders such as the concentration of allergen and quantity of dust/area varying more than 10 fold at different sites within a room. There is, however no data to directly show that such samples relate to individual personal exposure. Others have attempted to measure aeroallergens on stationary filters using an air pump. With this method the amount of aeroallergen per time or volume differs markedly with degrees of dust disturbance and pump flow rates. Generally, measurement of settled and airborne dust correlate only weakly with one another, if at all. Outdoor allergen sources, such as fungal spores or fallen particles, are estimated and generalised with spoor traps.
The best available method generally used to measure personal exposure is to use filters worn on the upper body. These were developed for occupational sampling eg. for asbestos and coal. Although they have been used occasionally for allergens they cannot be widely applied. This application is limited by battery life, low flow rates, consequent small samples and the relatively high cost of such sampling devices. Such filters may not reflect what is actually being inhaled for several reasons. Firstly, spatial distribution of allergenic particles differs over small distances. For instance, in bed the face is close to the allergen source and the allergen may not travel to a filter a half metre away. Secondly, the collection of particles onto a vertical filter surface with a low constant face velocity is significantly different from such a collection involving variable airflow into a person's nostrils. Variables include changes in flow between and within each cycle of respiration and with exercise, and the effects of thermal body drafts, movement and wind.
Airborne allergens are mainly carried by large particles, although this varies with both the allergen involved and the circumstances. Mite allergens are mainly carried by mite faeces (&gt;90% allergen 10-40 .mu. particles); cat allergens with dander particles (.sup..about. 70% associated with &gt;.sup..about. 3 .mu. particles); fungal allergens depend upon the species and maturity (3 to 90 .mu.); pollen depending upon the species (15 to 60 .mu., mainly 20 to 30 .mu.). What is airborne is dynamic and changes with time; small particles, for instance, have lower settling speeds and remain airborne for longer.
The nose of humans and other mammalian species efficiently collects particles, such as dust, pollen, and bacteria, onto the mucosa by a combination of turbulence and impaction. Efficiency is determined by particle velocity, angular velocity, mass, size and shape of the particle and the route that the particle takes in the nose.
There have been reports (Pasricha J. S. & Abrol B. M. Ann. Allergy 1974; 32: 331-333; French Patent specifications 2,536,659, and 2,504,003; U.S. Pat. Nos. 4,401,117 and 5,117,820) of the insertion of a tube containing a filter such as a wire mesh sieve into the nose for the purpose of relief of inhalant allergy. The use of such a wire filter with a:pore size capable of removing most particles associated with allergy (ie. those &gt;5 .mu. diameter) could be expected to have high airflow resistance and to be uncomfortable to use. In addition, as such a filter becomes loaded with particles its resistance would increase making it more difficult to use. In addition particulate material collected by such filters would be more difficult to completely remove in an unadulterated (virgin) state and so would not be in a form suitable for direct analysis.